Multicenter studies are under way in Europe and the United States investigating an angle-supported phakic IOL for the treatment of high myopia.
"So far, patients have maintained best spectacle-corrected visual acuity (BSCVA) after implantation of this IOL," said Dr. Kohnen, professor of ophthalmology, Johann Wolfgang Goethe University, Frankfurt, Germany. "Data on endothelial cell density changes and cataract formation rates indicate there is adequate clearance between the implant and both the cornea and crystalline lens, and no safety concerns have emerged in the adverse event reporting."
This phakic IOL is a foldable, angle-supported implant constructed of the same biocompatible acrylic material as some pseudophakic IOLs (AcrySof, Alcon). It has a single-piece design.
"The surgery itself is very easy. It involves a clear cornea incision, injection of viscoelastic, delivery of the lens, and placement of the haptics in the angle," Dr. Kohnen said. "In my own patients, I have not performed any iridotomies."
Patients are eligible for the multicenter trials if they are aged at least 18 years and demonstrate stable refraction and good ocular health. Age-specific criteria exist for endothelial cell density. Anterior chamber depth must be 3.2 mm or larger, according to the U.S. study protocol and one European study, although a second European study allowed entry of eyes with an anterior chamber depth of 3.0 mm or larger. All eyes must have no more than 2.0 D of astigmatism.
The combined enrollment in the European phase II and III and U.S. FDA phase I trials is 323 patients. Among 112 eyes seen at 2 years, only one eye showed a loss of 2 or more lines of BSCVA, and in the subset of 58 eyes with preoperative BSCVA of 20/20 or better, only one had a postoperative BSCVA worse than 20/40 at 2 years.
Analysis of change from preoperative BSCVA showed that, at 2 years, most eyes had no change or an increase in BSCVA, whereas <3% of eyes had a 1-line loss.
"This benefit of increase in BSCVA is similar to what is seen with other phakic IOLs," said Dr. Kohnen.
At 6 months, 1 year, and 2 years, an average of 0.5 D of induced manifest cylinder was seen.
During the acute postoperative period up to 6 months, mean endothelial cell count decreased by 3.69% centrally and 4.05% in the periphery. Between 6 months and 1 year, losses of 0.19% centrally and 1.09% peripherally were seen. Analysis of data from patients seen at 6 months and 2 years showed mean losses of 0.91% in the center of the cornea and 0.94% in the periphery.
"Effect on endothelial cell count is an important safety parameter for an anterior chamber phakic IOL, and these changes are low compared with some other anterior chamber models," Dr. Kohnen said.
At 6 months, IOP was within 5 mm Hg of baseline in 95% of eyes. Among 221 recipients of the 6.0-mm optic model, no cases of endophthalmitis were seen, six eyes had elevated IOP that required treatment, and cataract had developed in three eyes.
"These cataracts were not related to the . . . phakic IOL, but rather all were the result of being implanted upside down. Because of its curvature, this IOL has the potential to cause cataract if it is placed incorrectly," Dr. Kohnen said.
Three eyes showed slight synechiae in the angle, and no cases of pupil ovalization were seen, he said.